Increased RPMs

[rhgoudeau]

I have a 1996 Mercury 115 on a '96 Ranger R70. I have noticed an increased RPM the last 2 times out, along with a decrease in speed. At WOT I am turning 5800rpm, and barely reaching 40mph. The boat used to turn 5200rpm and 42-44mph. I marked the prop hub, thinking it was spun, but the marks are still lined up. The prop looks in good shape. Any ideas on what could cause this?

 

[oldman570]

Re: Increased RPMs

A GPS and the tack should tell you the true speed and RPM. The electrial instruments running off the battery will sometims read wrong if there is a problem with the electrical charging system of the unit. Cleaning all wires and cables along with a load test of the battery could slove the trouble you are having. JMO
Oldman570

 

[CharlieB]

Re: Increased RPMs

Draw a line across the back end of the prop, inspect your line after your next outing to see if the barrel and the retaining nut have slipped at all.